You can get away without one, but may be inconvenient to not have one. Windows and old game installs will be a bit problematic, but doable.
Also any $20 SATA DVD-RW will do. $20 is hardly the difference between a 128GB and 256GB SSD.
Oh, its a laptop.
Not entirely sure. Depends whether your willing to get around the inconvenience of not having it built right in.